Purpose: :
The aim of this study was to determine if co-signaling betweenα1β1, α2β1, α4β1, and α5β1integrins regulatesthe contractile properties of TM cells.

Methods: :
Integrin binding studies were performed using a colorimetricassay to determine the number of TM cells bound to type IV collagenor fibronectin in the presence or absence of 25 µg/mlβ1, α1, α2, α5, and αVβ3 integrin blocking antibodies.To visually assess TM contractility, confluent or subconfluentcultures were incubated with or without 0.5 mg/ml of the HeparinII (HepII) binding domain of fibronectin and changes in actinfilaments were observed by fluorescence microscopy with Alexa488-phalloidin. In some experiments, cells were grown on varyingconcentrations of fibronectin or type IV collagen. In otherexperiments, cells were grown on glass coverslips with onlyendogenous matrix present. Contractility was quantitated byincubating TM cells grown on 1.25 mg/ml rat tail collagen Igels for 24 hrs with 0.5-4 mg/ml of HepII or the PPRARI andIDAPS peptides. Gels were then detached from the dishes andtheir diameters were measured at 1, 6, and 24 hrs.

Conclusions: :
Contractile properties of TM cells are determined by integrinco-signaling and the composition of the extracellular matrix.Activation of α4β1 and α1/α2/β1 integrins by the HepIIdomain and type IV collagen leads to a disruption of actin filaments.In contrast, activation of α4β1 and α5β1 integrins byHepII and fibronectin increases stress fiber formation. Thissuggests that upregulation of fibronectin expression could alteractin dynamics and contribute to glaucoma.